A differential device including a differential case rotatably arranged in a transmission case and a final driven gear mounted on this differential case is integrally incorporated into some automotive automatic transmissions (AT) or manual transmissions (MT). The differential device is provided, for the purpose of its lubrication, with a lubrication structure composed to pump up lubricating oil stored in the transmission case using rotation of the final driven gear to be supplied to gears, a rotating shaft, etc.
The above-mentioned lubrication structure is provided with a guide groove for guiding lubricating oil to the inner surface of the transmission case. When lubricating a pinion gear and a pinion shaft in the differential case via an inboard section (or a boss section) of the differential device, the guide groove is adapted to guide lubricating oil into a space between an oil seal and a bearing via such guide groove, thereby lubricating the inside of the differential device.
In this case, as described in Patent Documents 1 and 2, a spiral groove installed on an inner wall of the inboard section of the differential case leads such lubricating oil that has been guided into the space between the oil seal and the bearing into the differential case, using rotating power of the differential case, thereby lubricating a pinion gear, a pinion shaft, a side gear, etc.